Myotonic dystrophy (DM) is an inherited disease primarily affecting skeletal muscle. There are two forms of the disease: DM1 is caused by a CUG repeat expansion in the 3' untranslated region of the Dystrophia Myotonica Protein Kinase (DMPK) gene while DM2 results from a CCUG repeat expansion in an intron of the Zinc Finger Protein 9 (ZNF9) gene. Pathogenesis in both cases is caused principally by accumulation of toxic RNA species containing the expanded repeat. The mutant RNA sequesters Muscleblind, an RNA-binding protein important for processing of clinically relevant mRNAs. In addition, the mutant RNA induces aberrant expression of another RNA-binding protein, CUGBP1 through an unknown mechanism. This in turn impacts processing and decay of additional mRNAs. We will first examine how the toxic RNA species is metabolized by the cell with a view to eventually enhancing its removal. We will then move on to investigate the effects of CUGBP1 on two sets of mRNAs encoding proteins involved in myogenesis and in protein secretion. Finally, we will generate novel cell culture models from patient muscle cells and utilize them to discover changes in mRNA stability that occur in DM1. Overall, we hope to elucidate the fundamental molecular changes that occur in myotonic dystrophy and identify novel targets for future therapeutics.